CN102610531A - Method for preparing diamond-silicon composite package material - Google Patents

Abstract

The invention relates to a preparation method of a diamond-silicon composite packaging material with high thermal conductivity and low expansion, belonging to the field of electronic packaging materials. The steps are: ① uniformly mix diamond particles and silicon powder with a volume fraction of 40-70% and a small amount of sintering aid, and the sintering aid is Al or Ti powder; ② put the graphite mold containing the mixture into SPS, and pressurize at 20-30MPa and vacuum; ③ rapid sintering, the holding temperature is set at 1250~1370℃ during sintering, inert gas or vacuum is used during the sintering process, and the sintering pressure is 40~60MPa; The pressure is dropped to obtain a dense composite material without microcracks. The invention avoids problems such as diamond graphitization and silicon matrix oxidation caused by too long sintering time; various composite materials with different diamond contents can be obtained by changing the ratio of raw materials, and has strong operability and simple process. Moreover, the thermal conductivity of the prepared composite material is as high as 515W/mK, the thermal expansion is lower than 1.5×10 ^-6 /K, and the density is over 99.6%, which can be used in electronic packaging and other fields.

Description

A kind of preparation method of diamond-silicon composite packaging material

technical field

The invention belongs to the field of electronic packaging, and relates to a new preparation method of a diamond-silicon composite packaging material, in particular to a diamond-silicon composite with high density, high thermal conductivity and low thermal expansion coefficient prepared by spark plasma sintering and adding sintering aids. Packaging material method.

Background technique

With the rapid development of modern electronics and information technology, the heat dissipation performance requirements of base materials are also getting higher and higher, so it is of great practical significance to study electronic packaging materials with good comprehensive performance. With the continuous improvement of chip integration and the development of electronic packaging in the direction of miniaturization, light weight and high performance, the operating temperature of the circuit continues to rise, and the heating rate per unit volume of the system continues to increase. In order to obtain stable performance, heat dissipation conditions must be improved, and the importance of electronic packaging in the field of microelectronics is increasing, and the demand for new electronic packaging materials is also increasing.

High-quality diamond has the highest thermal conductivity and low thermal expansion coefficient, and the thermal conductivity can reach 2000W/mK. In addition, diamond has the characteristics of electrical insulation and low dielectric constant; a single diamond is not easy to be made into packaging materials, which is ideal Composite materials are prepared by using diamond particles as reinforcements. At present, there are more studies on copper, aluminum, silver and silicon as matrix materials to prepare diamond composite materials. Among them, copper or silver as matrix materials have problems such as low wettability, high thermal expansion coefficient and high density; Too large to apply. High-purity silicon material has low density, high thermal conductivity and low thermal expansion coefficient. The density is 2.33g/cm ³ , the thermal conductivity (TC) is 160W/mK, and the coefficients of thermal expansion , CTE) is 3.6×10 ^-6 /K; the wettability of silicon and diamond is good, and silicon carbide is formed at the interface of silicon and diamond during sintering, which reduces the interface thermal resistance. Therefore, the research on diamond-silicon composite materials is of great significance to the development and application of this material.

The problems in the preparation of diamond-silicon composite packaging materials mainly include: (1) It is difficult to prepare dense diamond-silicon composite packaging materials by general preparation methods, and the density of diamond-silicon composite materials prepared by pressureless or hot isostatic sintering are very low. The sintering density can be improved by adding sintering aids to the composite material, but the density is still not high; (2) Diamond is very easy to graphitize under high temperature conditions, and the sintering time is too long to make the diamond surface graphitize, reducing the performance of the composite material.

In recent years, diamond-silicon composites have only been prepared by pressure infiltration. Using this method to prepare diamond/silicon composite materials, because the preparation process requires extremely high vacuum and ultra-high pressure, the requirements for equipment are extremely high, and the manufacturing cost is extremely expensive, which largely limits the diamond/silicon composite electronic packaging. Applications of materials in electrical engineering.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a diamond-silicon composite packaging material. The composite material prepared by the method has a firm interface contact, a simple preparation process, and significantly improved density and thermal performance.

In order to achieve the above object, the technical side that the present invention adopts is: a kind of preparation method of diamond-silicon composite packaging material, it is characterized in that, this method comprises the following steps:

(1) uniformly mixing diamond particles, silicon powder and sintering aid, wherein the volume fraction of silicon powder is 40% to 70%, and the volume fraction of sintering aid is 0 to 10%;

(2) Put the graphite mold containing the above mixture into the discharge plasma sintering furnace, pressurize 20-30MPa and vacuumize;

(3) Rapid sintering, the holding temperature is set at 1250-1370°C during sintering, inert gas or vacuum is used in the sintering process, and the sintering pressure is 40-60MPa;

(4) After sintering, the sample is cooled with the furnace and the pressure is released below 1000°C to obtain a dense composite material without microcracks.

As an improvement of the above technical solution, in step (3), the holding time during the sintering process is 3-5 minutes, and the heating rate is 50-150° C./min.

As a further improvement of the above technical solution, the inert gas is argon, and the vacuum degree is less than 10Pa.

The sintering aid may preferably be Al powder or Ti powder.

The invention combines rapid sintering in a spark plasma sintering (SPS) furnace with powder metallurgy, optimizes process parameters and improves comprehensive performance of samples through component and process control. A silicon carbide transition layer is formed at the interface between silicon and diamond, which significantly reduces the interface thermal resistance; adding a small amount of sintering aid effectively improves the density of the sample. Specifically, technical effect of the present invention is as follows:

1) The diamond particles are evenly distributed, and the interface with the silicon matrix is clean and firm

In the present invention, the SPS rapid sintering method is adopted to make an in-situ chemical reaction between the diamond particles and the silicon powder to form a silicon carbide transition layer, and then the density of the sample is improved by adjusting the heating rate and the holding time. Adding a small amount of sintering aid is beneficial to reduce the sintering temperature and time; after sintering, the sample is cooled with the furnace and the pressure is released below 1000°C, which is conducive to sintering compactness and reducing microcracks. After process optimization, the samples obtained have high interfacial connection strength and no microscopic defects.

2) The synthesis temperature is low, the process and equipment are simple, and the comprehensive performance is good

In this process, the highest sintering temperature is 1370°C. Under vacuum (less than 10Pa) or argon atmosphere, the heating rate is fast and the holding time is short, which can densify the sample in a very short time and effectively prevent diamond graphitization. The overall synthesis process has the advantages of simple equipment and process, low synthesis temperature, etc., and the thermal conductivity of the prepared composite material is as high as 515W/mK, the thermal expansion is lower than 1.5×10 ^-6 /K, and the density is over 99.6%.

The main equipment used in the present invention is: spark plasma sintering furnace (SPS).

3) Optimize product performance

Combining the rapid sintering method and adding sintering aids, a diamond-silicon composite packaging material with low density, high thermal conductivity and low thermal expansion coefficient can be obtained. Among them, the thermal conductivity and thermal expansion coefficient of the material can be adjusted by adjusting the content of diamond particles. As the diamond content increases, the thermal conductivity increases and the thermal expansion coefficient decreases; the higher the grade of diamond particles, the higher the thermal conductivity of the composite material. The higher the ratio is; the material properties can also be adjusted by adjusting the size of diamond particles, but the increase in thermal conductivity is not obvious with the increase of diamond particle size.

Description of drawings

Fig. 1 is the cross-sectional SEM picture of the sample, wherein a) is the cross-sectional view of the sample of Example 2; b) is the cross-sectional view of the sample of Example 1; and c) is the cross-sectional view of the sample of Example 5.

Fig. 2 is the sample surface of Example 2, wherein a) is enlarged by 20 times, and b) is enlarged by 300 times.

Fig. 3 is the line scanning energy spectrum of the sample of Example 1, wherein a) is the cross section, and b) is the line energy spectrum from point A to point B.

Fig. 4 is the line scanning energy spectrum of the sample of Example 2, a) is the cross section, and b) is the line energy spectrum from point A to point B.

Fig. 5 is the SEM picture of the sample section of Example 3.

Fig. 6 is the SEM picture of the cross-section of the sample of Example 4.

Fig. 7 is the cross-sectional line scanning energy spectrum of the sample of Example 5, wherein a) is a cross-sectional view, and b) is a line energy spectrum from point A to point B.

Fig. 8 is the SEM image of the cross-section of the sample of Example 6.

Fig. 9 is the EDS energy spectrum of the cross-sectional micro-area of the sample of Example 5, wherein a) is a cross-sectional view, and b) is a black square micro-area energy spectrum.

Detailed ways

The working principle of the method of the present invention is: rapid sintering by discharge plasma, so that silicon matrix particles and diamond particles undergo an in-situ chemical reaction under the melting point of silicon during the sintering process to form an interfacial silicon carbide layer, and by adding a small amount of sintering aid and cooling When the pressure is controlled, a dense diamond-silicon composite material is obtained.

Conditions and process:

1) Preparation conditions and equipment

Spark plasma sintering furnace (SPS) was used for sintering, X-ray diffractometer (XRD) was used for phase identification, environmental electron microscope (SEM; LEO 1450VP) was used for microstructure observation and analysis, and L457 thermal constant tester was used for thermal conductivity test. The coefficient of thermal expansion adopts NETZSCH DIL402PC.

2) Selection of sintering process

The sintering temperature is 1250-1370°C, select different sintering temperatures according to different material systems, and keep it warm for 3-5 minutes, then cool the sample with the furnace and release the pressure below 1000°C, see the specific parameters in each example.

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The raw materials used in the present invention are as shown in table 1:

Table 1

Among them, FDP diamond is a lower-grade diamond, and MBD8 is a high-grade diamond.

Example 1:

Table 2 shows the selected material system and composition ratio:

The proportioning of table 2 raw materials

Mix FDP-type diamond powder with an average particle size of about 100 μm and high-purity silicon powder evenly. The mixed powder is placed in the mold of the discharge plasma sintering furnace. When the vacuum degree reaches 10Pa, it starts to sinter at a heating rate of 50°C/min. Heating to 1370°C, the holding time is 3min, the sintering pressure is 30-60MPa, then cool with the furnace and release the pressure below 1000°C. The obtained diamond-silicon composite material has a density of 2.96 g/cm ³ , a thermal conductivity of 302 W/mK, and a thermal expansion coefficient of 1.627×10 ^-6 /K.

Through XRD phase analysis, it was found that the sintered sample contained three phases of Diamond, SiC and Si; the sample was sintered densely, and there was no hole in the sample cross section (Fig. 3), the silicon carbide layer is at the interface of diamond and silicon.

Example 2:

This example and example 1 adopt the same mixed raw material, the mixed powder is in the discharge plasma sintering furnace mould, when the vacuum degree reaches 10Pa, stop the vacuum pump, fill it with argon, and when the gas pressure is 0.03MPa, it is at a heating rate of 50 ℃/min heating to 1370℃, holding time is 3min, sintering pressure is 30-60MPa, then cool with the furnace and release the pressure below 1000℃. The obtained diamond-silicon composite material has a density of 2.97g/cm ³ , a thermal conductivity of 346W/mK, and a thermal expansion coefficient of 1.553×10 ^-6 /K.

The sintered sample contains three phases of Diamond, SiC and Si through XRD phase analysis; the sample is densely sintered, and the sample surface (Figure 2) and section (Figure 1(a)) have no holes; combined with XRD phase analysis and sample section Line scan (Fig. 4), silicon carbide layer at the interface of diamond and silicon.

There is no difference in the microstructure of samples after sintering under different sintering conditions (vacuum, argon), but the samples prepared by sintering under argon have higher thermal conductivity and lower thermal expansion coefficient.

Example 3:

Table 2 shows the selected material system and composition ratio:

Table 3 Ratio of Raw Materials

The MBD8 type diamond powder with an average particle size of about 100 μm is mixed evenly with high-purity silicon powder, and the mixed powder is placed in a discharge plasma sintering furnace mold, and the sintering process is the same as that of Example 2. The obtained diamond-silicon composite material has a density of 2.972 g/cm ³ , a thermal conductivity of 497 W/mK, and a thermal expansion coefficient of 1.517×10 ^-6 /K.

The sintered sample contains three phases of Diamond, SiC and Si through XRD phase analysis; the sample is sintered densely, and the sample section (Figure 5) has no holes;

Under the same conditions, different grades of diamond particles are used as reinforcements, and the thermal conductivity of the composite material is significantly improved.

Example 4:

This example and Example 3 use the same raw material ratio, mix MBD8 type diamond micropowder with an average particle size of about 300 μm and high-purity silicon powder evenly, and mix the powder in the discharge plasma sintering furnace mold, sintering process and example 2 is the same. The obtained diamond-silicon composite material has a density of 2.975 g/cm ³ , a thermal conductivity of 515 W/mK, and a thermal expansion coefficient of 1.479×10 ^-6 /K.

The sintered sample contains three phases of Diamond, SiC and Si through XRD phase analysis; the sample is sintered densely, and the sample section (Figure 6) has no holes;

Under the same conditions, diamond particles with different particle sizes are used as reinforcements, and the thermal conductivity of the composite material increases with the increase of diamond particles.

Example 5:

Table 4 The ratio of Diamond-Si

The FDP type diamond powder with an average particle size of about 100 μm is mixed with high-purity silicon powder and a small amount of aluminum powder evenly, and the mixed powder is placed in a discharge plasma sintering furnace mold, and the sintering process is the same as in Example 2. The obtained diamond-silicon composite material has a density of 2.975 g/cm ³ , a thermal conductivity of 264 W/mK, and a thermal expansion coefficient of 1.559×10 ^-6 /K.

The sintered sample contains four phases of Diamond, SiC, Al and Si through XRD phase analysis; the sample is densely sintered, and the SEM image of the fracture surface of the sample (Figure 1(c)) and EDS energy spectrum analysis (Figure 7), from It can be seen from the figure that a small amount of metal Al added is mainly distributed at the interface between silicon and diamond.

Compared with Example 2, under the same process conditions, the added small amount of metal Al is mainly distributed at the interface between silicon and diamond, because the addition of metal aluminum reduces the melting point of silicon, thereby reducing the sintering temperature and improving the sintering density. The lower aluminum is all melted into liquid, the diffusion coefficient is relatively large, and all the aluminum diffuses to the interface between silicon and diamond, but because the added metal aluminum exits the interface in the form of second-phase impurities, it has a great hindering effect on thermal conductivity. Therefore, the thermal conductivity decreases correspondingly after adding metallic aluminum.

Example 6:

Table 4 Ratio of Diamond-Si

The MBD8 type diamond powder with an average particle size of about 100 μm is mixed evenly with high-purity silicon powder and a small amount of titanium powder, and the mixed powder is placed in a spark plasma sintering furnace mold, and the sintering process is the same as in Example 2. The obtained diamond-silicon composite material has a density of 2.99 g/cm ³ , a thermal conductivity of 505 W/mK, and a thermal expansion coefficient of 1.459×10 ^-6 /K.

The sintered sample contains four phases of Diamond, SiC, TiSi2 and Si through XRD phase analysis; the sample is densely sintered, and the fracture morphology SEM image of the sample (Figure 8) and EDS energy spectrum analysis (see Figure 9 (a), ( b)), wherein, in Fig. 9 (a), the composition content in the small box micro region is: Si, the mass fraction is 87.17Wt%, the atomic fraction is 92.05At%, Ti, the mass fraction is 12.83Wt%, the atomic fraction 07.95 At%. It can be seen from the figure that the added small amount of metal Ti is mainly dispersed in the composite material.

Compared with Example 3, under the same process conditions, a small amount of metal Ti powder added, because the addition of metal titanium reduces the melting point of silicon, thereby reducing the sintering temperature and improving the sintering density, so the thermal conductivity increases correspondingly after adding metal titanium.

Example 7:

Table 5 Ratio of Diamond-Si

In this example, when the vacuum degree reaches below 10Pa, stop the vacuum pump and fill it with argon. When the gas pressure is 0.03MPa, it is heated to 1250℃ at a heating rate of 150℃/min, the holding time is 3min, and the sintering pressure is 30MPa. Release the pressure below 1000°C. The obtained diamond-silicon composite material has a density of 2.78 g/cm ³ , a thermal conductivity of 235 W/mK, and a thermal expansion coefficient of 2.079×10 ^-6 /K.

Example 8:

Table 4 The ratio of Diamond-Si

In this example, when the vacuum degree reaches below 10Pa, stop the vacuum pump and fill it with argon. When the gas pressure is 0.03MPa, it is heated to 1250℃ at a heating rate of 150℃/min, the holding time is 3min, and the sintering pressure is 30MPa. Release the pressure below 1000°C. The obtained diamond-silicon composite material has a density of 2.6 g/cm ³ , a thermal conductivity of 206 W/mK, and a thermal expansion coefficient of 2.153×10 ^-6 /K.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (4)

1. a preparation method of diamond-silicon composite encapsulation material, is characterized in that, the method may further comprise the steps: (1) Evenly mix diamond particles, silicon powder and sintering aid, wherein the volume fraction of silicon powder is 40%~70%, and the volume fraction of sintering aid is 0~10%; (2) Put the graphite mold filled with the above mixture into the spark plasma sintering furnace, pressurize at 20~30MPa and evacuate; (3) Fast sintering, the holding temperature is set at 1250~1370°C during sintering, inert gas or vacuum is used in the sintering process, and the sintering pressure is 40~60MPa; (4) After sintering, the sample is cooled with the furnace and the pressure is released below 1000°C to obtain a dense composite material without microcracks. 2. The method for preparing a diamond-silicon composite packaging material according to claim 1, characterized in that: in step (3), the holding time during the sintering process is 3-5 minutes, and the heating rate is 50-150°C/min. 3. The method for preparing a diamond-silicon composite packaging material according to claim 1 or 2, characterized in that: in step (3), the inert gas is argon, and the degree of vacuum is less than 10 Pa. 4. The method for preparing a diamond-silicon composite packaging material according to claim 1 or 2, characterized in that: the sintering aid is Al powder or Ti powder.

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